A significant requirement in sub-half-micron high-performance semiconductor technologies is junction depth reduction in, for example, CMOS (complementary metal-oxide-semiconductor) source and drains and bipolar emitters and bases. Reducing the junction depth suppresses MOS (metal-oxide-semiconductor) transistor punchthrough leakage and minimizes short channel effects such as drain-induced barrier lowering (DIBL) in CMOS devices. Devices junctions with relatively high dopant concentrations, ultra-shallow depths (e.g., below 1000 .ANG.), low contact sheet resistances, and low junction leakage currents will be critical for advanced subquarter-micron technologies.
Rapid thermal gas phase doping (RTGPD) is one advanced manufacturing doping technique for low defect density ultra-shallow junction formation for 0.25 .mu.m and sub-0.25 .mu.m ULSI (ultra-large scale integration) semiconductor technologies. This doping method provides a wide range of surface concentrations and junction depths on both planar and high-aspect ratio trench surfaces. In addition, this doping method is compatible with advanced submicron IC (integrated circuit) process flows while offering reliable, high throughput, and low cost options for high quality ultra-shallow junction formation.
RTGPD involves a three step process based on surface chemical adsorption of dopant gas molecules. First, the native oxide of the silicon surface is removed. Then, an adsorbed dopant layer is formed on the silicon surface. Finally, solid phase diffusion of dopants from the adsorbed layer into the silicon substrate is accomplished. Dopants are incorporated into the silicon substrate by diffusion in an oxygen-free atmosphere at a relatively low temperature. This process differs from conventional diffusion in which dopant diffusion is performed in an oxygen-rich ambient. Ultra-shallow junctions (e.g., junction depths of 700 .ANG.) with excellent electrical characteristics (e.g., leakage current less than 2 .times.10.sup.-16 A/.mu.m.sup.2) have been achieved. In an effort to deal with uniformity problems both inter-wafer and intra-wafer, complicated gas distribution systems have been developed. However, these problems with uniformity have not been satisfactorily solved. Accordingly, there is a need for a RTGPD system that improves dopant uniformity both interwafer and intra-wafer.